Effects of hydroxyl radical and sulfhydryl reagents on the open probability of the purified cardiac ryanodine receptor channel incorporated into planar lipid bilayers.

We examine the effect of hydroxyl radical on the ion permeability of the ryanodine receptor, a calcium releasing channel of sarcoplasmic reticulum. The cardiac ryanodine receptor, purified from pig heart, was reconstituted to proteoliposomes and then incorporated into a planar bilayer membrane. A single channel activity with a conductance of 724 pS in 900/200 mM (cis/trans) KC1 and an ion selectivity of PK:PCl = 1:0.08 was observed. These characteristics are similar to those observed by the incorporation of the channel through sarcoplasmic reticulum vesicles. Hydroxyl radicals chemically generated by the reaction of H2O2 and Cu(ethylenediamine)2 at the cis compartment increased the open probability of the channel. Treatment with SH oxidizing reagents from the cis compartment also increased the open probability, and dithiothreitol, a SH reducing agent, reversed the effect. These findings suggest that hydroxyl radicals react with some SH groups of the ryanodine receptor and increase the Ca2+ release from sarcoplasmic reticulum through the ryanodine receptor.